1. Field of the Invention
The invention relates to an actuating device for a differential lock, preferably a frictional lock, comprising an actuator piston arranged in a pressure chamber on the pressure side of a pump and acting on the differential lock when loaded by the hydraulic medium conveyed by the pump.
2. Description of the Related Art
A differential is known in which a rotor pump, driven by a differential speed (i.e., revolutions per minute or rpm) between the wheel axle and the differential housing, conveys oil into a piston housing in which a piston is axially slidably supported. When pressure is built up by the pump, the piston acts onto a lamella packet which effects by friction the transmission of the drive moment onto the vehicle wheels. A valve with a constant aperture cross-section mounted within the piston provides a differential rpm-dependent torque transmission. The valve makes it possible that the oil flows in a directed manner into the lamella space so that the pressure build-up behind the piston is made dependent on the conveyed oil volume. The constant aperture cross-section ensures a proper function of the lamella lock only within a narrow temperature range because the viscosity of the oil changes greatly with the temperature.
It is an object of the present invention to configure an actuating device of the aforementioned kind such that the lock operates properly within a wide temperature range.
In accordance with the present invention, this is achieved in that at least one conduit opens into the pressure chamber, has at least one temperature-dependent throttle element and is connected with a tank for the hydraulic medium (pressure medium).
In accordance with the present invention, the temperature-dependent throttle element ensures that the aperture cross-section will change as a function of the temperature of the hydraulic medium. When the temperature of the hydraulic medium increases, its viscosity is decreased and the pressure-medium becomes thinner. In this case, the aperture cross-section is reduced by the temperature-dependent throttle element. At low temperatures and thus a greater viscosity of the hydraulic medium, the aperture cross-section is enlarged by the temperature-dependent throttle element so that even at low temperatures a sufficient volume flow of the hydraulic medium is ensured. The throttle element forms a temperature-compensated valve in order to compensate the temperature dependency of the hydraulic medium viscosity.